Electric dryer power reduction ???

I had mentioned in another thread that I thought it should be possible to reduce the power consumption in half by half wave rectifying the power to the heating element.
I bought a 200A diode pack and installed it today and can confirm that the initial test says it can be done. I will continue to monitor it and blindly test it on "Her indoors"
Power has been reduced from 5200W to 2300W....the motor seems to draw around 500W from 1 "phase"
I decided to put the diode here in the schematic as it was convenient in the control panel


And here is the diode pack I used - Diode pack

And here is how it looked. If you do it, try to be more professional than me LOL.
THIS IS A HACKY TEST.

Very cool. I have a solar and wind power dryer... it only works on hot dry days though?

The power has been reduced by a factor of two. But it should now take twice as long to boil the same amount of water out of the same clothes! Total energy consummed will be (ideally) the same. Is the intent to reduce the demand by 2 and allow for smaller inverters?

Best way to lower power consumption with a dryer: get one with a heatpump.

Actually, you end up using more energy as the drum motor has to run 2x longer and you still need the same BTU's to remove the water, just will take 2X longer.

I do like this idea, filed away for future use.

I have a number of meaty opto-coupled triac boards intended to driven by an Arduino or similar. Could be used to actively throttle heating appliances according to available energy

Our specific application would be when running with the grid down. The EPS output of our Sofar hybrid is limited to 3kW (4kW surge) so running the lights, TV, PCs and 2.2 kW kettle puts it near the line. Being able to auto-throttle the kettle would work and allow operation of the microwave too.

At present overloading the EPS fires up the genset and moves all the load to it, much better to wait a bit longer for my tea!

Solar Guppy said:

Actually, you end up using more energy as the drum motor has to run 2x longer and you still need the same BTU's to remove the water, just will take 2X longer.

Click to expand...

This
Will use more energy per load.
But less continuous draw during the load.

Solar Guppy said:

Actually, you end up using more energy as the drum motor has to run 2x longer and you still need the same BTU's to remove the water, just will take 2X longer.

Click to expand...

This could be the case, I will try to figure out month to month usage on it. I have Emporia monitoring.

Madco said:

The power has been reduced by a factor of two. But it should now take twice as long to boil the same amount of water out of the same clothes! Total energy consummed will be (ideally) the same. Is the intent to reduce the demand by 2 and allow for smaller inverters?

Click to expand...

Yes this is the general idea of the test.

BartHenry said:

Very cool. I have a solar and wind power dryer... it only works on hot dry days though?

Click to expand...

My Grandmother told me clothes would still dry below freezing on a sunny day. Does take longer.

Solar Guppy said:

Actually, you end up using more energy as the drum motor has to run 2x longer and you still need the same BTU's to remove the water, just will take 2X longer.

Click to expand...

I wonder if it would be really two times as long. You’re gonna have to account for the more air that will be circulated to assist in drying.

Best thing I’ve found is to have a washer that has an insane spin cycle to get most of the water out to begin with. Some older LG’s with direct drive have that. Thing sounds like a turbine spooling up.

So how hot does the pack get?
Using diode to reduce power (only half cycle of the AC is being used) is commonly used on the hair dryer.
Same idea is used on incandescent lamp.

Danke said:

I wonder if it would be really two times as long. You’re gonna have to account for the more air that will be circulated to assist in drying.

Click to expand...

Our dryer, and I assume most, cycles the heater on/off rapidly to maintain temperature after initial heat up which is 10-15 minutes. I would expect after reaching temperature the heater would simply spend more time on than off and cycle less. Good idea, thanks for sharing I’m going to try it.

Quattrohead said:

I had mentioned in another thread that I thought it should be possible to reduce the power consumption in half by half wave rectifying the power to the heating element.
I bought a 200A diode pack and installed it today and can confirm that the initial test says it can be done. I will continue to monitor it and blindly test it on "Her indoors"
Power has been reduced from 5200W to 2300W....the motor seems to draw around 500W from 1 "phase"
I decided to put the diode here in the schematic as it was convenient in the control panel

View attachment 141777
And here is the diode pack I used - Diode pack

Click to expand...

How many hours have you run it that way so far?

MajicDiver said:

Our dryer, and I assume most, cycles the heater on/off rapidly to maintain temperature after initial heat up which is 10-15 minutes. I would expect after reaching temperature the heater would simply spend more time on than off and cycle less. Good idea, thanks for sharing I’m going to try it.

Click to expand...

This. It isn't constant the whole time, so this mod may make it take longer to heat up initially but much less instantaneous power to do it. Maintaining temp should be ok, at least on lower temp drying (not sure about hot, we almost never use that).

I'm going to stick with the physics and thermo on this one. It is still going to take the same energy to effect the phase change of liquid water to water vapor. I would argue that dropping the power applied to the heating element by a factor of two will increase the drying time by a factor of two. That will cause the drum motor to run twice as long, and if it burns 500W, then the overall power consumption to dry the same clothes with the same water content will increase by 500W. The peak demand will drop by half the heating element wattage.

That seems consistent with the whole energy star concept. If this saved energy, all dryer manufacturers would have been required to do this long ago. Manufacturers would have incorporated on their own anyway as a marketing ploy.

The air circulation is required to get rid of air saturated with water vapor, otherwise the clothes wouldn't dry at all even given a really hot interior temperature. I would guess that the air flow has been optimized to transport the saturated air and reducing the power inputto the element blows that optimization.

Overall, this reduces peak demand - good in that it possibly decrease the size of an inverter and good if you're using utility power on a TOU rate structure. The net energy to do the job will increase however.

Oops, should have said if on utility power and you have a demand charge!

The heating element is not 100% duty cycle. Listening to our dryer on low cycling the heater on and off (the relay clicks audibly) I have no doubt that it could maintain temperature with half the wattage but double the duty cycle. Higher dry temps may be an issue though.

Energy star doesn't really care about instantaneous power draw, but average power usage. So 1000W for 30 min vs 500W for an hour is the same to them. Adding a diode array is just going to increase cost (and another part to possibly break) to the manufacturer without any real incentive to them. Plus, I could see it not working well at high tenp drying (although you could put a relay in the circuit to bypass the diode when set to high temp, but again you're increasing costs/complexity).